Iron Embrasures for the Batteries on Morris Island

Another problem faced by the engineers and artillerists preparing the breaching batteries on Morris Island was the embrasures through which the guns pointed over the parapets. As the embrasure is an opening in the fortification, these are always weak points in the works. But without them, the gun crew must work the gun over the parapet and might be exposed to enemy fire. In defensive works, with more time devoted to perfection of the opening, engineers used wood planking to define the embrasure. Normally, for earthworks such as seen around Vicksburg, Petersburg, or other siege lines of the Civil War era, the engineers used gabions filled with dirt.

But the nature of Morris Island presented a problem with that practice, as Major Thomas Brooks explained in Note No. 12 of his report:

Gabions, fascines, and hurdle work, when used for revetting the cheeks of embrasures, were found to leak the fine dry sand used in the construction of our works, unless filled or backed with sandbags. This remedy adds to the expense and labor, and is, besides, not very durable. Sods suitable for revetting are very scarce on this coast.

Sand-bags alone lasted a long time in Battery Hays, but its guns were fired at an elevation of 5° and upward. These high elevations gave a far less injurious cone of blast than low ones. The raw hides used for lining sand-bag embrasures were soon blown out (particularly by the Wiard gun), in spite of our efforts to make them fast by means of notched pickets.

The Ruby looks picked over. And more than just damage done while recovering the blockade runner’s goods. She was practically scrapped in place as the Federal engineers turned salvaged materials into something to resolve the embrasure problem:

To overcome these difficulties, a boiler or sheet-iron casing or lining was made from iron plates obtained from the wreck of an iron ship (a blockade-runner) which came ashore at Light-House Inlet. The splay, the dimensions of the throat, size of cheeks, length and inclination of sole, and thickness of plates used, were varied to suit the case. For direct firing, the splay may be 25°, or even less.

To set the casing, the genouillère is first finished, and the sole of the embrasure given its proper slope. On this sole is placed the iron casing, its directrix having the proper direction. Sand-bag merlons were built on each side, to which the lining was anchored by means of wires and crooked iron rods which were made fast to its cheeks and rings.

Brooks provided an illustration of these improvised embrasures.

Brooks recorded the iron as a quarter-inch thick, weighing 10.4 pounds per square foot. Eight of these went in to the second parallel. The illustration helps explain a mantlet configuration used for one of the gun positions in Battery Rosecrans:

This mantlet is of bullet-proof iron plate, arranged as a hanging door, which closes the throat of the embrasure. In this door is a cut or slot for the double purpose of allowing the rammer and sponge staves to pass through when loading, and for sighting the piece. A small scantling of hard wood, with a rope attached to its upper end, is made fast to one side of the door, and acts as a lever to raise the door when the gun is fired. The swing bar of 1-inch round iron, upon which the hinges of the door are hung, has a collar at each end, to enable the cheeks of the carriage to resist lateral pressure. The sole was given a counter slope of 5°. The wings prevent the casing from being carried out by the force of the blast.

The one gun position supplied with a mantlet was active against Fort Sumter during the bombardments through September. Because of the elevations required to reach that target, the gun crew might otherwise be exposed to Confederate sharpshooters. The mantlet arrangement allowed the crew to work with some measure of safety.

In conclusion, Brooks suggested, “The satisfactory results obtained from the use of these casings indicates that sheet and boiler iron should form part of the siege material furnished for military operations in a sandy country.” He added that the plate was later easily converted to Sibley stoves during the winter months.

3 responses to “Iron Embrasures for the Batteries on Morris Island”

This explains a lot about the picked-over carcass of the Ruby in that wonderful photo. I had wondered why there didn’t appear to be any hull plates or framing left around the remains of the engine room. I think that the embrasures he illustrates were almost certainly made of sheet-iron hull plates, though, not boiler plates. While of similar thickness, boiler plates would have been curved in various ways, as shown by the surviving boiler in the background of the photo. Hull plates, on the other hand, were relatively flat and square.
The Banshee, built in early 1863, was the first steel-hulled runner, and had hull plates just 1/8″ thick- said to be “half the thickness of the usual iron plates” of contemporary blockade runners. They were so thin that they buckled on the transatlantic journey and had to be repaired in Nassau. In 1861 boiler plate was produced for the U.S. Navy in 3/16, 1/4, 3/8 and 5/16 thicknesses (according to the US Senate document publishing all the naval supply contracts for 1860-61), usually in sheets 4-fleet long by 30 inches wide.
By comparison the Tredegar Iron Works in Richmond could only roll plates 8 inches wide by ten feet long, which were a maximum of 2 inches thick for the armor plate installed on the CSS Virginia. Armor plate made for the USS New Ironsides was 4 1/2 inches thick, and the railroad iron used on southern ironclads later in the war was 2 1/2 inches wide by 1 1/2 inches thick. So quarter-iron sheet iron was barely bullet-proof by comparison.

An inventive idea by Brooks- but I’m glad I wasn’t one of the enlisted men out there in the sun busting the heads off rivets to canabalize the Ruby that June and July!